1. Technical Field of the Invention
This invention relates generally to radio frequency integrated circuits and more particularly to on-chip differential inductors used in such radio frequency integrated circuits.
2. Description of Related Art
Communication systems are known to support wireless and wire lined communications between wireless and/or wire lined communication devices. Such communication systems range from national and/or international cellular telephone systems to the Internet to point-to-point in-home wireless networks. Each type of communication system is constructed, and hence operates, in accordance with one or more communication standards. For instance, wireless communication systems may operate in accordance with one or more standards including, but not limited to, IEEE 802.11, Bluetooth, advanced mobile phone services (AMPS), digital AMPS, global system for mobile communications (GSM), code division multiple access (CDMA), local multi-point distribution systems (LMDS), multi-channel-multi-point distribution systems (MMDS), and/or variations thereof.
Depending on the type of wireless communication system, a wireless communication device, such as a cellular telephone, two-way radio, personal digital assistant (PDA), personal computer (PC), laptop computer, home entertainment equipment, et cetera communicates directly or indirectly with other wireless communication devices. For direct communications (also known as point-to-point communications), the participating wireless communication devices tune their receivers and transmitters to the same channel or channels (e.g., one of the plurality of radio frequency (RF) carriers of the wireless communication system) and communicate over that channel(s). For indirect wireless communications, each wireless communication device communicates directly with an associated base station (e.g., for cellular services) and/or an associated access point (e.g., for an in-home or in-building wireless network) via an assigned channel. To complete a communication connection between the wireless communication devices, the associated base stations and/or associated access points communicate with each other directly, via a system controller, via the public switch telephone network, via the Internet, and/or via some other wide area network.
For each wireless communication device to participate in wireless communications, it includes a built-in radio transceiver (i.e., receiver and transmitter) or is coupled to an associated radio transceiver (e.g., a station for in-home and/or in-building wireless communication networks, RF modem, etc.). As is known, the transmitter includes a data modulation stage, one or more intermediate frequency stages, and a power amplifier. The data modulation stage converts raw data into baseband signals in accordance with the particular wireless communication standard. The one or more intermediate frequency stages mix the baseband signals with one or more local oscillations to produce RF signals. The power amplifier amplifies the RF signals prior to transmission via an antenna.
As is also known, the receiver is coupled to the antenna and includes a low noise amplifier, one or more intermediate frequency stages, a filtering stage, and a data recovery stage. The low noise amplifier receives inbound RF signals via the antenna and amplifies them. The one or more intermediate frequency stages mix the amplified RF signal with one or more local oscillations to convert the amplified RF signals into baseband signals or an intermediate frequency (IF) signals. The filtering stage filters the baseband signals or the IF signals to attenuate unwanted out of band signals to produce filtered signals. The data recovery stage recovers raw data from the filtered signals in accordance with the particular wireless communication standard.
Many of the components in the radio receiver and radio transmitter include inductors. For example, mixers in the IF stages of both the receiver and transmitter, the power amplifier, a voltage control oscillator of a local oscillation module, the low noise amplifier, and the filters each include one or more inductors. When the radio receiver and/or radio transmitter are implemented as integrated circuits, the fabrication of on-chip inductors for components used within the receiver and/or transmitter is an important design consideration. Currently, the state of the art of on-chip inductor design in a CMOS process provides one with few practical design choices. For instance, one could choose a spiral wound single ended inductor (square or octagon in shape), which provides up to approximately 20 nano Henries. The inductance value is limited due to the capacitance of the inductor, which, in combination with the inductance, establishes the self-resonating frequency.
For differential applications, one could choose a pair of single ended inductors or a spiral wound square differential inductor. Typically, the spiral wound square differential inductor is preferred over a pair of single ended inductors because it is smaller in size and has a higher quality factor (Q).
While the current state of the art of on-chip inductors provides practical design choices, they are insufficient for optimal integrated circuit design, especially for radio frequency integrated circuits (RFIC). For example, the spiral wound square differential inductor in many IC designs is not an optimal shape for efficient IC layout. Further, increasing the quality factor of an on-chip inductor is beneficial in many applications.
Therefore, a need exists for an on-chip differential inductor that has an improved quality factor and may be shaped for optimal integrated circuit (IC) layout.